Polymerization and interpolymerization of ethylene



Patented Dec. 18, 1945 POLYMERIZATION AND INTERPOLYMEB- IZATION OFETHYLENE .R eglnald George Robert Bacon, Manchester, and

Raymond B. Richards, Northwlch, England, asslgnors to Imperial ChemicalIndustries Limited, a corporation of Great Britain No Drawing.Application February 14, 1944-, Se-

rial No. 522,370. In Great Britain January 6,

Claims.

This invention relates to the polymerizationgof ethylene and theinterpolymerization and telomerization of ethylene with one or morecompounds.

It'is already known that ethylene can be polymerized at very highpressures to yield polythene, if desired using oxygen as a catalyst. Itis also known that at high pressures ethylene can be interpolymerizedwith other organic compounds containing carbon-carbon double bonds andcapable of forming polymers. More recently it has been shown that thesereactions can be carried out in the presence of an aqueous medium byemulsifying ethylene, or mixtures thereof with other .polymerizablesubstances, in an aqueous solution of an emulsifying agent and heatingthe emulsion to a temperature of 60-150 C. after adding oxygen orsubstances supplying oxygen, generally at pressures of 800-1500atmospheres. InU. S. Serial No. 328,770 of M. N. Brubaker, filed April9, 1940 is described and claimed a process whereby ethylene ispolymerized alone or interpolymerized with other polymerizable organiccompounds having ethylenic unsaturation, in intimate contact withwaterand a per-compound at a pressure greater than 50 atmospheres and atemperature of 45-l50 C. The per-compounds used to induce the reactionto take place are peroxides, per-acids and per-salts, for examplepersulphates.

Two further classes of products can also be obtained from ethylene byanalogous processes.

One of these classes is obtainable by inter-polymerizing ethylene witheither carbon monoxide or formaldehyde or a formaldehyde-yieldingsubstance, by subjecting them together to an elevated temperature andpressure in the presence of a peroxy compound and preferably in thepresence of a liquid medium such as water. Processes for producing theseinterpolymers are described in U. 8. Serial Nos. 449,765 of M. N.Brubaker, filed July 4, 1942 and449,'779 of W. E. Hanford, filed July 4,1942 respectively. Products of the, remaining class are called telomersand are obtained by subjecting ethylene (or other polymerizablealiphatic monoolefinic hydrocarbons) and a tolegen as hereinafterdefined to conditions which normally give rise to polymerization of theolefine; such conditions include subjecting them to an elevatedtemperature and pressure in the presence of a per-compound and anaqueous medium. A process for carrying out such a reaction where thetelogens are saturated estadrides of inorganic acids is described in U.8. Serial No. 438,466 of W. E. Hanford et al., filed April 10, 1942; bysaturated estadride" is meant esters or anhydrides of real orhypothetical inorganic acids, which are free fromcarbon-carbonunsaturatlon. This process is also applicable to reactionsof an aldehyde or a ketone free from carbon-carbon unsaturation andhaving at least one alpha hydrogen atom. I

' The object of the present invention is to provide a process forcarrying out any of the above reactions more rapidly than has hithertobeen possible at a given temperature and pressure, whereby the reactionscan be conducted at lower temperatures and pressures than those hithertopossible, and whereby there can be produced products of, a higheraverage molecular weight than those hitherto obtainable. Moreover it isnow practicable to obtain products which could hitherto only be made byworking in the lower part of the operating temperature range andconsequently at an extremely slow speed.

We have found that reactions involving the formation of polymericmaterials from ethylene, either alone or in combination with othersubstances, in the presence of an aqueous medium and of a per-compound,are facilitated and accelerated by the presence of a water-soluble saltof an oxy-acid of sulphur with reducing properties.

According to the present invention, we provide a process which comprisessubjecting ethylene alone or with at least one of the compoundscomprising compounds having at least one ethylenic double bond carbonmonoxide, formaldehyde or a formaldehyde-yielding substance, a saturatedestadride of an inorganic acid, or an aldehyde or ketone free fromcarbon-carbon unsaturation and having at least one alpha hydrogen atom,to an elevated temperature and pressure in the presence of an aqueousmedium and a small amount of a per-compound, together with awater-soluble salt of an oxy-acidof sulphur with reducing properties.

Compounds having at least one ethylenic double bond which may be used orpolymerizable compounds containing the group C=CH, for example vinylchloride, unsymmetrical ,dichloroethylene; styrene, butene; vinylethers, vinyl ketones, vinyl esters; acrylic and methacrylic acids andtheir esters, amides and nitrilcs; and dienes for example butadiene.

As a formaldehyde-yielding substance we may use substances which yieldformaldehyde by thermal or catalytic decomposition. Examples of suchsubstances are formalin, paraformaldehyde, polyoxymethylene,a-trioxymethylene, methylal and other formals, and hexamethylenetetramine.

As saturated estadrides we may use chloroform, carbon tetrachloride,methyl chloroiodide and other halogen derivatives of hydrocarbons;chloralhydrate; chloracetic acid and other saturated halogenatedcarboxylic acids and their esters; dimethyl sulphate, ethylorthosilicate and other esters of inorganic acids especially of sulphur,phosphorus and silicon.

As aldehydes.and ketones free from carboncarbon unsaturation andcontaining at least one alpha hydrogen atom, we may use paraldehyde,propionaldehyde; acetone, cyclohexanone. and other substances containingthe structure CHCO preferably those containing from 2 to 8 carbon atoms.

Per-compounds which may be used are those compounds which are eitherformed by the action of hydrogen peroxide on ordinary acids, or elsegive rise to hydrogen peroxide on treatment with dilute sulphuric acids.Examples of per-compounds are the peroxides such as benzoyl peroxide andacetyl peroxide; persulphates such as the ammonium, sodium and potassiumsalts of persulphuric acid; perborates and percarbonates. The amount ofper-compound is generally at least 0.1% and up to by weight of the totalliquid charge, preferably 0.3-1

Examples of suitable water-soluble salts of oxy.. acids of sulphur withreducing properties are sulphites, dithionites, sulphoxylates,pyrosulphites, bisulphites, and thiosulphates, in particular the sodiumsalts. The quantity of such salts will usually be less than the amountwhich is chemically equivalent to the amount of per-compound present,and is generally, but not always, 0.005-5%, preferably 0.020.2%, byweight of the total liquid charge. e

The aqueous medium employed may be water alone, or water containingother materials such as dispersing agents, buffers or other reagents foradjusting and controlling the pH of the medium, and organic liquids suchas isooctane and toluene.

The temperature employed when making polymers of ethylene alone isgenerally between 50 and 120 C. and preferably between 70 and 100 C.,and the pressure generally exceeds 500 atmospheres, preferably beingbetween 800 and 2000 atmospheres. For the manufacture of interpolymersand telomers the same temperature ranges are applicable, but ratherlower pressures may be used depending on the second com onent; pressuresexceeding 50 atmospheres, and generally exceeding 200 atmospheres, areused. The process maybe carried out continuously, by continuousintroduction of the raw materials to the reaction vessel and removal ofthe mixture containing the product from the reaction vessel, the productbeing isolated from the mixture for example by filtration, if necessaryaftercoagulation. Vigorous agitation is desirable during the process inorder to maintain homogeneous reaction conditions, and his alsodesirable to. remove the heat evolved during the reaction, preferably byexternal cooling, The reaction is preferably carried out in a vesselfabricated of or lined with corrosion-resistant material, for examplestainless steel. The reaction is preferably carried'out in the absenceof appreciable amounts of oxygen, and for this purpose the air initiallypresent in the reaction vessel may be displacedor removed beforeintroducing the reaction mixture. Also, to avoid contamination withoxygen it is advisable that the raw materials employed be in a highdegree of purity.

' process. Depending on the conditions of poly-- The products obtainedare essentially of the same character as those obtained by the priormerization and the initial materials employed, they may vary fromliquids and semi-solid substances through waxes to hard; fibrous orrubbery masses of high molecular weight.

The invention is illustrated but not restricted by the followingexamples in which all parts are by weixht.

Example 1 A stainless steelbomb is half-filled with 400 parts of water.Three parts of benzoyl'peroxide and0. part of sodium dithionite areintroduced, and ethylene containing less than 10 parts per million ofoxygen is compressed into the bomb.

The pressure and temperature are then raised to 750 atmospheres and 75C. respectively, and the contents of the .bomb are stirred for 4 hours.The pressure is then released and the bomb is opened. 80 parts of atough white solid of molecular weight 17,000 are obtained by separatingit from the aqueous phase. For comparison, when the above procedure isrepeated without the addition of the sodium dithionite the yield is only40 parts of a similar-solid of molecular weight 15,000.

Example 2 of it being 5, 7 or 9 carbon atom telomers.

In the absence of the sodium dithionite, the same weight of productrequired 10 hours reaction time.

Example 3 A silver-lined bomb is charged with 95- parts of 37% formalin,0.5 part of benzoyl peroxide and 0.1 part of sodium bisulphite. The bombis closed, heated to 75 C..and ethylene is admitted so that a pressureof 900 atmospheres is'maintained for 2 hours. After this time the bombis cooled, the pressure is released, and the reaction mixture isdischarged and filtered. The product is 15 parts of a white solid whichmelts at 100 C. and has an ethylene/formaldehyde ratio of 11.

In the absence of sodium bisulphite the same product is only obtained in10 hours reaction time.

Example A silver-lined bombof capacity 100 parts of water is chargedwith parts of water, 0.4 part of sodium persulphate and 0.4 port ofsodium thiosulphate. The bomb is closed and carbon monoxide admitted toa totalpressure of atmospheres. The total pressure is then raised to 600atmospheres by compressing ethylene into the bomb. The bomb is thenheated to C. and more ethylene is admitted to raise the total pressureto 1200 atmospheres at this temperature. After maintaining thetemperature at 100 C. for 2 hours the pressure is released and thereaction mixture is discharged and filtered. The product is 9 parts of asolid whose melting point is in the region of 100 C. and which has anaethylenezcarbon monoxide ratio of 1.5:1.

with reducing properties is sodium hydrosulphite.

2. A process as claimed in claim 9 in which the water-soluble salt of anoxy-acid of sulphur with reducing properties is sodium bisulphite.

3. A process as claimed in claim 9 in which the water-soluble salt of anoxy-acidof sulphur with reducing properties is sodium hydrosulphate.

4. A process as'claimed in claim 9 in which the peroxy compound is analkali metal persul- Dhate.

5. A process as claimed in claim 9 in which the peroxy compound isbenzoyl peroxide.

6. A process as claimed in claim 9 carried out at a temperature of70-100 C. and a pressure of 800-2000 atmospheres.

7. A process as claimed .in claim 9 in which I the quantity ofwater-soluble salt of an oxy-acid of sulphur with reducing properties isless than is chemically equivalent to the amount ofpercompound present.

8. A process as claimed in claim 9 in which the reaction is carried outin the absence of appreciable quantities of oxygen.

. 9. A process for the manufacture of polymeric materials whichcomprises heating ethylene under a pressure of at least 50 atmospheresin the presence of an aqueous medium, from 0.1 to 5% of a peroxycompound, and rrom 0.005 to 5%. or a water-soluble salt of an oxy acidof sulphur. with reducing properties selected from the group consistingof sulphites, dithionites, sulphoxylates, pyrosulphites, bisull hites,and thiosulphates.

10. A Process for the manufacture of polymeric materials which comprisesheating ethylene under a pressure or at least 50 atmospheresin thepresence 01' an aqueous medium and a peroxy compound while in thepresence of a water-soluble salt of an oxy acid of sulphur with reducinproperties selected from the group consisting of sulphites, dithionites,sulphoxylates, Pyrosulphites, bisulphites, and thiosulphates, therebeing present from 0.3 to 1% by weight of the peroxy compound and 'aquantity of the salt or an oxy acid of sulphur less than is chemicallyequivalent

